The present invention relates to a vehicle provided with an infinitely variable transmission which can make a speed ratio infinite, wherein a variation of inertia torque during a speed change is compensated to improve drivability.
A continuously variable transmission (CVT) is controlled so that a speed ratio (value obtained by dividing a transmission input rotation speed by a transmission output rotation speed) is a target speed ratio determined from the throttle opening of an engine, and the vehicle speed.
If the speed ratio changes with speed change, the rotation speed of the engine will change and an inertia torque will arise. This inertia torque affects drivability during the speed change. For example, since the engine torque decreases due to a negative inertia torque when a downshift which increases engine speed is performed, the driver has the feeling that torque is insufficient. Conversely, as the engine torque increases due to a positive inertia torque when an upshift which reduces the engine speed is performed, the driver has the feeling that the torque is excessive.
JP-A-H11-20512 published by the Japanese Patent Office in 1999 discloses a technique of suppressing the variation of engine torque due to the inertia torque during a speed change, by adjusting the engine torque according to the inertia torque during the speed change. According to this technique, the inertia torque during speed change is calculated from the variation rate of the speed ratio and the output rotation speed of the transmission, and the engine torque is adjusted so that the inertia torque may be eliminated.
Further, in an infinitely variable transmission (IVT) which realizes an infinite speed ratio by combining a continuously variable transmission with a planetary gear set, the above-mentioned inertia torque compensation is necessary.
However, in the IVT, the power transfer route inside the transmission changes over in a power recirculation mode used when the vehicle is stationary or when it is moving at low speed, and in a CVT direct mode used when the vehicle is moving forward at high speed. Accordingly, the moment of inertia of the power train is different in these two modes, so the above-mentioned prior art technique is inapplicable as it is.
It is therefore an object of this invention to improve drivability during a speed change by calculating the inertia torque at the time of speed change with high accuracy, and compensating the inertia torque in a vehicle provided with an IVT.
In order to achieve above object, this invention provides a vehicle control system, comprising an engine, an infinitely variable transmission connected to the engine, the transmission comprising a continuously variable speed change mechanism, a planetary gear set, and an operation mode change-over mechanism which changes over between a power recirculation mode wherein power is transmitted through the speed change mechanism and planetary gear set, and a CVT direct mode wherein power is transmitted only through the speed change mechanism, a drive shaft to which the torque of the engine is transmitted via the transmission, and a microprocessor. The microprocessor is programmed to determine whether the operation mode of the transmission is the power recirculation mode or the CVT direct mode, select an inertia torque computing equation corresponding to the operation mode of the transmission, compute the inertia torque accompanying a speed change of the transmission using the selected inertia torque computing equation, and adjust the torque of the engine so that the computed inertia torque is compensated.